Time-scaling methods are used to compress and expand video and audio signals. It is well known in the art how to speed up and slow down video. This is done in video disk players and video cassette recorders routinely. Since the video is encoded on a frame-by-frame basis, the rate of frame display is slowed down or sped up, and each frame is displayed on a display device for a corresponding longer or shorter period, respectively.
It is also well known in the art how to speed up and slow down audio by itself without significant distortion. Slowing down audio, or [0]time scale “expansion,” overlaps the same audio block and performs an add function for essentially duplicating time. Various techniques most commonly used to accomplish acceleration, on the other hand, include Time Domain Harmonic Scaling (TDHS), dropping frames, and Synchronize Overlap and Add (SOLA) algorithms. While simply dropping frames results in gaps in the audio signals and associated frequency distortion, algorithms such as SOLA substantially preserve the frequency pitch of the digital audio signals.
Prior Art FIG. 1 illustrates the SOLA algorithm 100, in accordance with the prior art. SOLA begins by “chunking” input into frames. Thereafter, a rough estimate of the output-frame spacing is calculated based on a target compression rate. This final spacing is set to the position of the maximum cross correlation near the desired spacing. SOLA creates output audio by cross fading frames, using this new frame offset.
As can be seen from the above discussion, the prior art includes numerous techniques for variable speed playback of digital audio alone and variable speed playback of digital video alone.
However, there is a need for a system and method which uses the foregoing techniques to provide a way for a user who is playing back digital audio/video (A/V) content from a digital medium [i.e. digital video disc (DVD)] to vary the speed of presentation and be presented with synchronized, high quality simultaneous audio and video. This would allow the user to cue the information based on either the audio or the video content, or both, and to slow down or speed up the rate of presentation and still perceive both the audio and the video.
Many makers of digital mediums (i.e. DVDs) are currently implementing particular compression algorithms. Representative compression algorithms are MPEG and Dolby® AC-3. Those of skill in the art will appreciate that the MPEG and AC-3 algorithms are well known, evolving standards. Accordingly, reference herein to these standards will be understood to mean the video and audio compression standards as they existed at the time of the earliest effective filing date of the present application, and as they have evolved to date, and as they continue to evolve over the term of any patent that issues herefrom.
In particular, the AC-3 standard was adopted as the audio standard for North American High-Definition Television (HDTV) systems. The AC-3 standard has recently been applied to the DVD's, Direct Broadcasting System (DBS), Set Top Box (STB), digital cable, etc. The AC-3 compression algorithm also uses the human psychoacoustic characteristic as a basis for audio compression. In order to implement a compression algorithm such as the AC-3 standard, AC-3 encoders and decoders are often required. Various prior art systems currently incorporate such encoders and decoders, but not for the purpose of playing back high quality synchronized, time-scaled content from digital mediums (i.e. DVDs).
Prior Art FIG. 2 illustrates a DVD playback system 200, in accordance with the prior art. As shown, a DVD player 202 is provided which is adapted for reading video signals and audio signals from a DVD. Most frequently, such video signals take the form of MPEG video signals, while the audio signals include AC-3 audio signals.
Also included is a video decoder 204 for decoding the MPEG video signals for producing a video output signal. Still yet, an audio decoder 206 is included for decoding the AC-3 audio signals for producing an uncompressed digital audio output signal. Optionally, the audio decoder 206 may be bypassed for producing a digital audio output signal still encoded in the compressed format, in the manner shown.
Unfortunately, the DVD playback system 200 simply does not include the ability to speed up and slow down audio in conjunction with speeding up and slow downing video read from a digital medium (i.e. DVD) in a quality manner.
Prior Art FIG. 3 illustrates a more general system 300 including the components of the DVD playback system 200, but utilizing a Von Neumann-type architecture. The architecture of such a system 300 may be found in game units such as the XBOX® manufactured by Microsoft® Corporation.
As shown, a DVD player 302, a video decoder 304, and an AC-3 decoder 306 are provided, similar to those of the DVD playback system 200 of Prior Art FIG. 2. Further provided is an AC-3 encoder 308 for producing a compressed and encoded digital audio signal from an uncompressed digital audio signal. Still yet, a central processing unit (CPU) 310 may be provided for performing general processing or functionally implement the decoder or encoder processors. Associated therewith is graphics processing hardware 312 for accelerating graphics processing. Still yet, memory 314 is provided for storage purposes. All of the foregoing components may be interconnected via a bus 318, as shown.
Currently, components such as the AC-3 encoder 308 are used in the context of the aforementioned game units for generating compressed digital audio during the play of games, etc. However, there lacks any ability to speed up and slow down digital audio in conjunction with speeding up and slow downing video read from a digital medium (i.e. DVD) in a quality manner.
Prior Art FIG. 4 illustrates a flow of operation 400 that may be carried out using the general system 300 of Prior Art FIG. 3. As shown, a DVD player 302, a video decoder 304, an AC-3 decoder 306, an AC-3 encoder 308, a CPU 310, and graphics processing hardware 312 are provided.
As shown, the DVD player 302 may be used for reading video signals and audio signals from a DVD. Most frequently, such video signals take the form of MPEG video signals, while the audio signals include AC-3 audio signals. The MPEG video signals are fed to the video decoder 304 for generating video output signals. Still yet, the AC-3 encoded audio signals are output directly as encoded digital audio, or optionally sent to the AC-3 decoder 306 and output as an uncompressed digital audio signal.
In use, the AC-3 decoder 306 decodes the AC-3 audio signals for producing uncompressed digital audio output signals. Further, the CPU 310 may be used to process other various video and audio signals in conjunction with the graphics processor hardware 312 and the AC-3 encoder 308, respectively. Thus, the CPU 310 is adapted to produce video output signals, uncompressed digital audio signals, and compressed digital audio signals utilizing the graphics processor hardware 312 and the AC-3 encoder 308 in the manner shown. Each of the aforementioned video output signals, uncompressed digital audio signals, and compressed digital audio signals may be selectively outputted utilizing multiplexers 402 in the manner shown.
Unfortunately, the general system 400 of Prior Art FIG. 4 fails to process the uncompressed digital audio signals outputted from the AC-3 decoder 306 for time-scaling purposes. Again, there lacks any ability to speed up and slow down audio in conjunction with speeding up and slow downing video read from a digital medium (i.e. DVD) in a quality manner.
There is thus a need for a system and method of speeding up and slow downing audio in conjunction with speeding up and slow downing video read from a digital medium (i.e. DVD) in a quality manner.